_________________"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY

Funny I should be working on my DSR when I spot this post. I was wondering if anyone could tell me what the orange wire wrapped around the red/yellow wire is for on the PT.

Thanks

_________________...I for one, sure would appreciate the return of intelligent conversation, spirit of assistance and the simple yet effective ignoring of those who can't seem to hang with that...Best regards,rob

I don't believe that the power tranny is original in this Showman. Notice that there are TWO lines from the PT to ground. An orange one and a red-yellow one. This should only be in an amp that has the center-tap (CT) of the heater line grounded. And not one with two 100-ohm balancing resistors on the pilot lamp. Having the heater CT grounded AND the two 100-ohm resistors effectively cuts the heater voltage in half.

The Red-Yellow line is the CT of the main voltage going to the rectifier. It is properly grounded.

The schematic & layout of the AB763 Showman's heater setup versus the AA768 ---you can see the taps off the PT at the lower right corner of the schematic. Notice how the AB763 has an internal ground point on the heater taps. And the AA768 doesn't?

And how this AA768 Showman has 100-ohm resistors from the heater line/pilot lamp to ground and the AB763 doesn't?

The Orange line is an external center tap off the heaters. And should not have been connected with those 100-ohm resistors in place. These resistors shows severe signs of heat damage, esp on the non-Fender solder point to the ground. this is prolly due to excessive current draw to compensate for the low heater voltage --- due to the miss-wiring.

I think this is an AA769 you have there because my DSR is a 69' and the schematic shows the two 100 ohm resistors on the heater lines and the 3.3k on the bias supply line. I'm also guessing since my PT looks the same wire wise as your PT that it must be an original tranny unless mine was swapped out with one identical to yours.

Anyway when I ohm out the orange wire I get 10 meg or so to any other PT wire or ground so it's open which makes sense with the 100 ohm resistors in circuit. The whole reason I ask is because this wire broke off the ground connection in my amp and I was wondering what it could be for.

Please slap me now if I'm derailing this thread.

Thanks

Arc

_________________...I for one, sure would appreciate the return of intelligent conversation, spirit of assistance and the simple yet effective ignoring of those who can't seem to hang with that...Best regards,rob

The orange wire is a shield line. Which apparently is not connected to the case of the PT (I tried testing it). Apparently hooked to an internal isolation shield inside the PT, without continuity to the case.

Thanks for that. I was hoping the orange wire was for SOMETHING! If I didn't have my DSR apart right now I'd do a voltage check for you but if I recall the last time I looked at mine they were all pretty close. The problem I have with my DSR is that I can easily tolerate the volume up at 10 where I can't tolerate my Marshall 50 watt head past 2. The DSR sounds great but I haven't figured out why the output is so low. I figured I get started on it now but first I want to get the chassis straightened out. Somewhere in this amps life it took a spill and the trannys yanked the chassis out from flat.

I hope you can give me some advice as you move along with your repair and I appreciate what you have helped me with already.

Thanks again.

Arc

_________________...I for one, sure would appreciate the return of intelligent conversation, spirit of assistance and the simple yet effective ignoring of those who can't seem to hang with that...Best regards,rob

3.) Replaced the grid-to-ground 68k-ohm resistors on the 6L6GCs, the 47k-ohm resistors on the PI plates. Most couplling caps --- several of those generic OEM brown drop passed more than a 1-2 VDC. And the components under the doghosue.

4.) Sockets showed sign of heat damage. Brittle, with pieces falling off. UNfortunately, this later era SF had 1-inch socket holes & it's hard to find good NOS 1-inch sockets. So had to use Russian made ceramic ones.

5.) R&R the heater lines. And new 100-ohm resistors on the heater-to-ground pseudo-CT. OEM ones read 225 and 310 ohms.

5.) Oh, I put in 2-amp Slow-Blow fuse (amp rec 2.5 amps).

Plate voltage is 468 VDC at the anode. And the idle bias reads -50.2 VDC at the those 68K-ohm resistors. Idle bias current trhough EH 6L6GC = 40-43mA per tube at 468 VDC.

Equals around 19.5-19.8 watts idle dissipation per tube.

Tone is very clean. Loud (though a four by 10-inch cab). A little "tight." Prolly due to components still breaking-in.

_________________"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY

No one could ask for a better amp tech. He kept in contact very regularly and took great pains to describe to me, in detail, everything that he was doing and why. I got many many e-mails, photos and phones call throughout the whole process. On my side of this situation, it was a very pleasant experience and nobody could expect or ask for more.

The orange wire is a shield line. Which apparently is not connected to the case of the PT (I tried testing it). Apparently hooked to an internal isolation shield inside the PT, without continuity to the case.